The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations to develop mobile communications systems. Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies, which is also being developed into a 4G technology. The most common form of UMTS uses Wideband-CDMA as the underlying air interface. Evolved UMTS Terrestrial Radio Access (E-UTRA) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. E-UTRA is the successor to High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) technologies specified in 3GPP releases 5, 6 and 7. Unlike HSPA, LTE's E-UTRA is a new air interface system unrelated to W-CDMA. E-UTRA uses Orthogonal Frequency Division Multiplexing (OFDM) and multiple-input multiple-output (MIMO) antenna technology to support more users, higher data rates and lower processing power required on each handset.
In 3GPP Release-8, work is ongoing to improve the uplink performance in what is called the CELL_FACH state. At the radio resource control (RRC) level, two basic operation modes of a mobile radio terminal, sometimes called a user equipment (UE), are idle mode and connected mode as shown in FIG. 1. The connected mode is divided into service states, which define what kind of physical radio channels a UE is using. FIG. 1 also shows the main RRC service states in the connected mode and the transitions between states and between modes. In the CELL_FACH state, no dedicated physical channel is allocated to the UE, but the random access and forward access common channels (RACH and FACH respectively) are used instead. The UE is known on a cell level (i.e., it has a cell id), has a protocol layer 2 connection (including media access control (MAC) and radio link control (RLC) protocol layers), but does not have dedicated physical (PHY) layer 1 radio resources. Instead, common physical layer radio resources are shared between mobile terminals in the CELL_FACH state for transmitting both signaling messages and small amounts of user plane data to UE's in the CELL_FACH state.
An uplink improvement planned for future cellular radio systems is activation in the CELL_FACH state of an uplink enhanced-dedicated channel (E-DCH) physical channel established with HSUPA. The E-DCH is normally used as a dedicated physical layer channel in CELL_DCH state (shown in FIG. 1) with one separate E-DCH resource allocated per UE. This can be performed by using a pool of E-DCH resources that can be temporarily assigned to a UE in the CELL_FACH state. Such a pool of E-DCH resources is termed “common E-DCH resources.” The E-DCH resources may be managed by a Radio Network Controller (RNC) in 3G UMTS type systems, but the pool of common E-DCH resources may be managed by the radio base station, sometimes referred to as a NodeB, to speed up the allocation of radio resources by not having to involve an RNC or other management node in the allocation procedure.
The number of common E-DCH resource configurations available in each base station cell is limited by available air interface resources and the number of radio receivers in the base station. The common E-DCH resource configuration is a set of parameters that defines the E-DCH resource, e.g., an uplink scrambling code, a F-DPCH code and offset, and E-DCH HARQ Acknowledgement Indicator Channel (E-HICH) and E-DCH Relative Grant Channel (E-RGCH) Information. The common E-DCH resource assignment scheme may also place requirements on how many E-DCH radio resources can be assigned at one time. Given that the set of common E-DCH resources and configurations available in each cell is limited, E-DCH resources need to be efficiently used and managed.
The technology in this application provides a method and apparatus for efficiently using E-DCH resources. A UE can release common E-DCH resources very quickly after a completed transmission. In addition or alternatively, a base station may release common E-DCH configurations from the network side to free up common E-DCH resources for use by other UEs. Various signaling schemes for quickly and effectively releasing common E-DCH resources between a UE and a base station are also provided. For example, existing signaling fields already in use in a CELL_DCH service state may be given a different meaning for UEs in a CELL_FACH service state so that common E-DCH resources are quickly and effectively released. Alternatively, a new message or a new field in an existing message may be used.
In one example embodiment, a UE in a CELL_FACH state releases an E-DCH resource allocated to the UE. When the UE determines that the common E-DCH resource allocated to the UE should be released, it signals to the base station release of the common E-DCH resource on existing protocol layer 1 or protocol layer 2 message fields already in use in a CELL_DCH state for other purposes. In one example scenario, the common E-DCH resource is released when the UE detects that its transmit buffer is empty. The UE may signal the release to the base station by including a Scheduling Information (SI) field in a last Media Access Control (MAC) Packet Data Unit (PDU) stored in the transmit buffer which is sent by the UE using the common E-DCH resource. If the transmit buffer is an E-DCH buffer, the SI field indicates a total E-DCH buffer status of zero. The UE can signal the release of the common E-DCH resource to the base station by setting an E-DCH-Transport Format Combination Identifier (E-TFCI) or a happy bit on a physical layer control channel to indicate release of the common E-DCH resource.
In one example variation, the UE releases the common E-DCH resource upon receiving an Acknowledgement (ACK) for all outstanding Hybrid Automatic Repeat Request (HARQ) processes associated with the UE's transmissions to the base station using the allocated common E-DCH resource or upon reaching a predetermined maximum number of HARQ transmissions. The common E-DCH resource may also be released when an HARQ reordering timer has expired for the last MAC PDU.
In another example embodiment, a radio base station releases a common E-DCH resource allocated for use by a UE in a CELL_FACH state. The radio base station determines that the common E-DCH resource allocated to the UE should be released and then sends a grant on a common E-DCH resource grant channel indicating an inactive grant for the UE as a command to the UE to release the common E-DCH resource. The inactive grant on the common E-DCH resource grant channel means that the release is executed even though there may be outstanding unfinished Hybrid Automatic Repeat Request (HARQ) processes associated with the UE's transmissions to the base station using the allocated common E-DCH resource.
In another example embodiment, a release timer may be set with a predetermined value, and the common E-DCH resource may be released upon expiry of the release timer. The common E-DCH resource release timer is started when the common E-DCH resource is assigned to a UE and stopped when uplink transmission has been detected from the UE on the common E-DCH resource. The common E-DCH resource release timer may be implemented in the UE, the base station, or both.